Transition from ferromagnetic to noncollinear to paramagnetic state with increasing Ru concentration in FeRu films

TL;DR

This study investigates how increasing Ru concentration in FeRu films causes a transition from ferromagnetic to noncollinear and then to paramagnetic states, highlighting structural changes and magnetic behavior relevant for thin-film device applications.

Contribution

It provides new insights into the structural and magnetic phase transitions in FeRu alloys with varying Ru content, supported by experimental and atomistic modeling.

Findings

Ru induces noncollinear magnetic order in BCC FeRu alloys

Hexagonal FeRu alloys become paramagnetic with high Ru content

Magnetic domain size decreases with increasing Ru concentration

Abstract

The structural and magnetic properties of sputter-deposited Fe$_{100-x}$Ru$_x$ films were studied for $x \leq 50$. The crystal structure of Fe$_{100-x}$Ru$_x$ is shown to be predominantly body-centered cubic for $x<13$ and to undergo a gradual transition to hexagonal close-packed in the concentration range $13 \lesssim x \lesssim 20$. Magnetic measurements indicate that the addition of Ru induces a noncollinear magnetic order in the body-centered cubic FeRu alloys, while the hexagonal close-packed FeRu alloys exhibit paramagnetic behavior. Increasing the Ru concentration in body-centered cubic FeRu alloys decreases the size of magnetic domains, approaching the size of magnetic grains. A simple atomistic model was used to show that antiferromagnetic coupling of Fe atoms across Ru atoms can be responsible for inducing noncollinear order in the FeRu cubic structures. Magnetic multilayer structures used in thin-film magnetic devices make extensive use of both Fe and Ru layers. Our results reveal that the presence of even a small amount of Ru in Fe influences the magnetic order of Fe, which could impact the performance of these devices.